fix(Collection): fix session leak in parallelCollectonScan

Makes sure that parallelCollectionScan does not create an implicit
session, so that it does not leak or expire.

Author: daprahamian

lib/collection.js

@@ -2590,7 +2590,7 @@ Collection.prototype.parallelCollectionScan = function(options, callback) {
   options.promiseLibrary = this.s.promiseLibrary;
 
   return executeOperation(this.s.topology, parallelCollectionScan, [this, options, callback], {
-    returnsCursor: true
+    skipSessions: true
   });
 };